1. Field of the Invention
The present invention relates to an apparatus for treating semiconductor wafers, and more particularly, the present invention relates to an apparatus for treating a wafer in which a thermal reflector is provided above a wafer support.
2. Description of the Related Art
Thin films comprised of various types of materials are formed on wafers during the sequential processes for manufacturing a semiconductor device. To ensure high yields and operationally superior devices, the thin film materials should exhibit good step coverage, that is, a uniform thickness over every region, regardless of the surface pattern of an underlying layer.
Uniform step coverage requires that all process conditions employed in the formation of thin films be uniformly maintained, from source gas supply to wafer temperature. Moreover, the structure of the thin film forming apparatus itself may affect the uniformity of the thin film.
FIG. 1 is a cross sectional schematic view of a conventional thin film forming apparatus. The conventional apparatus includes a chamber 10 for housing the wafers to isolate them from the outside environment during a process of forming thin films. The apparatus also includes a susceptor 16 formed on the bottom surface of the chamber 10, and a shower head 18. The susceptor 16 supports the wafer 24 along a wafer-load region 20, and a heater 22 is provided under the wafer-load region 20. The heater 22 maintains the wafer 24 at a preferred temperature conducive to the formation of a thin film on the wafer 24. In addition, the heater 22 may be used to anneal the wafer 24 after forming the thin film thereon.
The shower head 18 directs the source gas, which is needed to form the thin film material, toward the wafer 24 on the wafer load region 20. Any residual gases are discharged through an outlet 28 formed at the bottom of the chamber 10 by a pump 26 provided outside of the chamber 10. Inlet/outlet region 30 allows the wafer 24 to be transported into and out of the chamber 10.
With the conventional thin film forming apparatus, by-products are created during the process and these by-products adhere to the chamber wall and aggregate to become particles 32. In addition, if a multi-chamber apparatus is used, when the wafer is transferred within the confines of the multi-chamber apparatus, the by-products or the thin film materials which exist near the wafer-load region of the susceptor may also be transferred.
Accordingly, with the conventional film forming apparatus, particles 32 adhered to the chamber wall may break apart and be deposited on the wafer, or by-products created by transfer of the wafer may be adhered to the wafer, resulting in undesirable impurities being included on the thin film deposited on the wafer. This degrades the thin film characteristics, and ultimately degrades the semiconductor device function when the inferior thin film is applied on the semiconductor device.
Another problem with the conventional apparatus concerns the heating/annealing of the wafer. After the thin film material is formed on the wafer, an annealing step to stabilize the thin film is performed at a temperature higher than that used for forming the thin film. The wafer temperature is a function of the thermal energy supplied from a heater block (e.g., 22 in FIG. 1), but the thermal energy distribution is not uniform when the heater block is initially heating up. Accordingly, the temperature distribution along the wafer is not uniform. When the temperature of the wafer is increased by using the heater, the temperature only stabilizes after oscillating above and below the preferred temperature. Thus it takes time to obtain a uniform temperature distribution along a wafer during the annealing process, which reduces the throughput.
Accordingly, it is an object of the present invention to provide an apparatus for surface treatment of a wafer which prevents impure particles from being deposited onto the wafer, especially during the formation of a thin film.
It is another object of the present invention to quickly obtain a uniform wafer-temperature distribution during an annealing process after the formation of a thin film, thereby improving the performance and increasing the productivity of semiconductor devices.
To achieve these and other objects, the present invention provides a wafer heating device having a wafer-load region at an upper portion, a shower head opposing the wafer-load region for ejecting/directing a source gas toward the wafer surface, and a reflecting apparatus positioned between the shower head and the heating device for reflecting thermal energy radiated from the heating device back toward the wafer-load region. There is also provided a pumping device for controlling the air pressure in the chamber and for discharging by-products formed within the chamber.
The reflecting apparatus includes a reflector positioned above and opposing the wafer-load region, and a supporter for supporting the reflector. The reflector may have a flattened reflecting surface facing toward the wafer-load region, or a semi-spherical type reflector having a concave mirror facing toward the wafer-load region.
The reflector can be controlled to move upward and downward in response to the thin film formation process and the annealing process. The movable reflector is connected via the supporter to a driver outside the chamber. The supporter includes a first cylinder connected to the driver and a second cylinder connected to the driver through the first cylinder at one end, and connected to the reflector at the other end. The supporter is symmetrically arranged around the shower head or the heating device.
The thin film forming apparatus according to the present invention is provided therein with a reflecting apparatus above the susceptor, thereby preventing particles from being deposited on the wafer during the formation of the thin film. In addition, even without applying additional power to the heater during the thin film forming process to the annealing process, the wafer temperature can be increased and stabilized in preparation for the annealing, and is uniformly maintained. Furthermore, even if additional temperature controls are necessary, the reflector shortens the time required to reached a stabilized increased temperature, thereby increasing the productivity of the semiconductor device manufacturing process.